Set Ollama sampling and runtime options per request (num_ctx, num_predict, seed, temperature, stop) via the options object
domain: ollama.com · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Pass an options object on /api/generate or /api/chat, e.g. options: {"num_ctx": 8192, "num_predict": 512, "temperature": 0.2, "seed": 42, "stop": ["\n", "user:"]}. Any Modelfile PARAMETER can be set here at runtime, overriding the model's defaults for that request only.
Key options and defaults: temperature 0.8, top_k 40, top_p 0.9, min_p 0.0, repeat_last_n 64, repeat_penalty 1.1-style penalties, num_predict -1 (unlimited), num_ctx 2048 by default (server default can be raised with OLLAMA_CONTEXT_LENGTH, e.g. OLLAMA_CONTEXT_LENGTH=8192 ollama serve).
For reproducible outputs set both seed (fixed int) and temperature 0.
Hardware-ish knobs also live in options: num_gpu, main_gpu, num_thread, num_batch, use_mmap, numa.
To change defaults permanently, bake PARAMETER lines into a Modelfile / the parameters dict of /api/create instead of sending options every call.
Known gotchas
num_ctx silently truncates: if prompt + history exceed it, the oldest content is dropped without error — raise num_ctx (or OLLAMA_CONTEXT_LENGTH) for long conversations, RAM permitting.
Required RAM scales with OLLAMA_NUM_PARALLEL * context length — a big num_ctx multiplied across parallel slots can OOM the server.
Options go inside the options object; putting temperature at the top level of the request body is silently ignored.
seed alone isn't enough for determinism if temperature > 0 sampling differences remain across versions/hardware.
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